1. Field of the Invention
The present invention relates to an active energy beam-curable composition which is quickly cured by irradiation with an active energy beam such as ultraviolet radiation and electron beam, which causes neither odor nor cloudiness even when the cured composition is heated, and which has a low viscosity with good operation performance. The present invention also relates to an ink which contains the energy beam-curable composition, and a printer which accommodates the ink.
2. Description of the Related Art
The active energy beam curing technique is extremely important in a variety of industries including, for example, wood coating, metal painting, and printing, because of various characteristics including, for example, the quick curing speed, the good operation performance generally brought about by the absence of solvent, and the extremely low amount of required energy. Especially, the photo-cationic polymerization is attractive, because of the sufficient possibility to realize a variety of chemical and physical characteristics by means of polymerization of various monomers. In the photo-cationic polymerization, the polymerization is not inhibited by oxygen. Therefore, it is unnecessary to carry out the polymerization in an inert atmosphere. The photo-cationic polymerization is advantageous in that the polymerization can be performed quickly and completely in the air.
However, the conventional active energy beam-curable composition involves the following problem. That is, when the active energy beam-curable composition is further heated after being subjected to coating and curing on a base material such as wood, metal, and paper, any odor is caused by the volatile component thereof, for example, any uncured remaining monomer.
When the active energy beam-curable composition is used at the inside of an instrument or the like, the following problem also arises. That is, when the active energy beam-curable composition itself undergoes a high temperature, any cloudiness appears in the instrument due to the volatile component of the active energy beam-curable composition.
Taking the handling of the active energy beam-curable composition into consideration, it is desirable that the active energy beam-curable composition itself has a low viscosity before being cured. Therefore, when the active energy beam-curable composition contains a photo-cationic polymerizable substance and a polymerization initiator, a low viscosity polymerizable substance such as vinyl ether is used as a diluent in order to lower the viscosity. However, when the low viscosity polymerizable substance such as vinyl ether is used, the following problem arises. That is, when the cured composition is heated as described above, then the volatilization occurs, and the odor and the cloudiness are caused.
The present invention has been made in order to solve the problems as described above, an object of which is to provide an active energy beam-curable composition which has a low viscosity with good operation performance, which avoids the appearance of the volatile component even when the active energy beam-curable composition is cured and heated thereafter, and which makes it possible to avoid the occurrence of the odor and the cloudiness, an ink containing the composition, and an ink discharging apparatus with an ink container which accommodates the ink.
According to a first aspect of the present invention, there is provided an active energy beam-curable composition comprising:
a photo-cationic polymerizable substance;
a photo-cationic polymerization initiator; and
a polymerizable compound having an ethylenic unsaturated double bond.
In the present invention, the active energy beam-curable composition, which comprises the photo-cationic polymerizable substance and the photo-cationic polymerization initiator, contains the polymerizable compound having the ethylenic unsaturated double bond. The polymerizable compound having the ethylenic unsaturated double bond may be, for example, monomethacrylate, dimethacrylate, monoacrylate, or diacrylate. It is considered that the polymerizable compound having the ethylenic unsaturated double bond as described above is polymerized by the irradiation with the active energy beam (radical polymerization), and the polymerizable compound having the ethylenic unsaturated double bond forms a bonding state by means of any chemical reaction together with the photo-cationic polymerizable substance. Therefore, even when the composition, which has been cured by the irradiation with the active energy beam, is heated again, then the volatile component, which is any remaining monomer, exists in an extremely small amount, and thus the odor and the cloudiness are scarcely caused. Further, the compound as described above has a relatively low viscosity. Therefore, it is easy to handle the active energy beam-curable composition.
In view of the prevention of the cloudiness and the odor which would be otherwise caused by the cured composition, the photo-cationic polymerizable substance preferably contains an epoxy resin compound. Especially, an alicyclic epoxy resin compound is preferred, because it enhances the crosslinking degree of the active energy beam-curable composition. Alternatively, the photo-cationic polymerizable substance may be an oxetane compound. When the oxetane compound is used, it is possible to more effectively avoid the cloudiness and the odor when the cured composition is heated.
The photo-cationic polymerization initiator may contain an onium salt. When the onium salt is used, then the crosslinking degree of the active energy beam-curable composition is enhanced, and it is possible to more effectively avoid the cloudiness and the odor when the cured composition is heated.
The active energy beam-curable composition may be a color or colorless (transparent) ink, for example, an ink to be preferably used for the ink-jet (or ink discharging) application. In this case, the composition may contain, for example, a coloring agent of a synthetic dye or a pigment, an inorganic filler, a surface-treating agent (a surfactant and/or a dispersing agent), a viscosity-adjusting agent, a treating agent, and an ultraviolet radiation-blocking agent, in addition to the photo-cationic polymerizable substance and the polymerization initiator. When the composition is used as the ink for the ink-jet application, the composition is prepared so that the viscosity of the composition upon discharging the ink from an ink jet head (ink discharging head) is 2 cps to 30 cps.
The content of the polymerizable compound having the ethylenic unsaturated double bond is preferably about 5% by weight to about 58% by weight, in view of the fact that the occurrence of the odor and the cloudiness is avoided. Further, when the composition is used for an ink head of an ink jet apparatus (or ink discharging apparatus) which performs photo-molding or photo-curing printing, the content of the polymerizable compound having the ethylenic unsaturated double bond is preferably about 10% by weight to about 48% by weight. The content of the polymerizable compound having the ethylenic unsaturated double bond affects the viscosity of the composition. Therefore, when the composition is used as the ink for the ink-jet application, the content is preferably adjusted within a range in which the viscosity of the composition upon discharging the ink from an ink jet head is 2 cps to 30 cps.
According to a second aspect of the present invention, there is provided an ink discharging apparatus comprising:
an ink discharging head which discharges an ink;
an ink tank which stores the ink to be supplied to the ink discharging head; and
a light source which is used to cure the discharged ink, wherein the ink comprises:
a photo-cationic polymerizable substance;
a photo-cationic polymerization initiator; and
a polymerizable compound having an ethylenic unsaturated double bond.
In the ink discharging apparatus of the present invention, the ink, which has been discharged by the ink discharging head, for example, onto the impermeable surface of those of wood, metal or the like, is cured with the light source such as the ultraviolet radiation. The ink contains the photo-cationic polymerizable substance, the photo-cationic polymerization initiator, and the polymerizable compound having the ethylenic unsaturated double bond. Therefore, the ink has a preferred viscosity to be discharged from the ink discharging head. Even when the cured ink is heated, neither odor nor cloudiness is caused. The ink discharging apparatus may be provided, for example, as a dispenser, a coater, and a printer. The ink tank may be an ink container fixedly provided in the apparatus or an ink cartridge which is replaceable.